Instead of mothballing NASA's aging shuttle fleet in 2010, two of the orbiters could be launched with SpaceHab's Research Double Modules in their respective cargo bays for living space.

The two shuttles would be connected in orbit - cargo bay to cargo bay - by a truss outfitted with a central rocket engine to provide the thrust necessary to leave Earth orbit. An inflatable connecting corridor between the two shuttle airlocks would provide astronaut access between the linked spacecraft.

Knight likens his plan as an evolved version of the Mars Direct plan advocated by Mars Society President Robert Zubrin, which also detailed a mission that used tethered modules and hinged on a crew's ability to generate their return fuel once they arrived at Mars.

Once underway, the spent rocket engine and its support truss could be jettisoned, and the connecting corridor and a cable tether linking the two space shuttles to extended outward a few hundred feet. The shuttles would then fire their thrusters in concert to enter a gentle spin that could provide slight gravity for the months-long flight through interplanetary space.

NASA's space shuttles aren't built to support crews for longer than just over a couple weeks at a time, though Knight suggests that regenerative life support systems like those recently delivered to the International Space Station could do the trick. Hydroponic gardens inside the living modules would boost crew food supplies in the plan. Periodic pit stops to resupply fuel and other expendables would be required along the way, necessitating some sort of freighter assist, he adds.

Landing challenge

But it's once the cobbled-together Mars ship arrives at the red planet that Knight's proposal takes a novel turn. Since NASA's 100-ton space shuttles are designed to glide through Earth's atmosphere during landings, they won't be able to handle well in the thinner atmosphere of Mars.

Knight suggests using massive parachutes.

"What I propose is the development of a very large parachute system that would be stowed in each of the orbiter's payload bays," he writes in the paper. "Each orbiter would then enter the Mars atmosphere and descend ballistically (like Apollo and Soyuz capsules), deploy its parachute system, and land wheels down with surely a pretty good thump - even with the planet's gravity just 38 percent of Earth's."

This idea explicitly is meant

Quote:

as a springboard for more creative ideas for the future of human spaceflight.

Why would someone want to send 2 shuttles on a one-way trip to mars?
What's the reason for all this extended living space in the payload bay, hydroponic gardens etc. when no humans will be on board (since there is no way of going back)? "First settlers on Mars"... yeah right, like somebody would have a reason to live in a "fishtank" on Mars basically doing nothing but waiting if (maybe) a few decades somebody else will come to take them home.

And then this concept needs some soft of "freighter" that accompanies the shuttles along the way for supplies? What's the reason then for taking the shuttles in the first place? Not to mention the lack of radiation shielding, that makes the shuttles even less suited for the job.

I do understand, that this is meant as a thought experiment to spur creative thinking but this rather sounds like daydreaming.

What would I suggest?
Intensify RD of (solar) electric propulsion, demonstrate (with a small probe) that this can be used to reach Mars and return to Earth way faster than with chemical propulsion. Then build a dedicated "Mars-Ship" with electric propulsion (or maybe VASIMR).

The difficulty of reaching Mars would decrease substantially if the trip no longer takes 6 months one-way but instead only a few weeks.

what about abstracting from the circumstance that theShuttles are applied to the more general circumstance that existing reusable vehicles are applied? This might free capacities of R&D for tasks yet to be solved.

What about applying the find that the diameter of a magnetic shield around a vehicle doesn't need to be larger than 100 meters to protect astronauts against the solarwind and si ilar particles? The generator would be small enough to mount several of them to the two Shuttles.

What about adding alander and a tanker to keep the Shuttles in orbit, cancel the jettisonation and thus enable return by the Shuttles and land by them n Earth then?